Apple Mail inbox message disappear after a week

Quit Mail.

Back up all data. That means you know you can restore the Mail database, no matter what happens.

Triple-click the text on the line below to select it:

~/Library/Mail/V2/MailData/Envelope Index

Copy the selected text to the Clipboard (command-C). In the Finder, select

Go ▹ Go to Folder

from the menu bar. Paste into the box that opens (command-V), then press return.

A Finder window will open with a file selected. Move the selected file to the Desktop, leaving the window open. Other files in the folder may have names that begin with "Envelope Index". Move those files, if any, to the Trash. Relaunch Mail. It should prompt you to re-import your messages. You may get a warning that the index is corrupt and that Mail has to quit. Click OK.

Test. If Mail now works as expected, you can delete the file you moved to the Desktop. If you get a warning that the file is in use when you try to empty the Trash, log out and log back in.

Now the story has changed. The messages are not disappearing; they're being moved to the Trash. Mail doesn't do that under any circumstances, so if that's really what is happening, some third-party software that you installed must be doing it.

Then please follow the instructions to rebuild the envelope index. That procedure is no harder to carry out than what you do with the computer every day.

I'll take a guess here, in your Mail app, under view menu, is the Organize by Conversation is checked?

It's up to you, it's just that I tought for a second that when it's organize by conversation, all the e-mails from a conversation are grouped into the same email in your inbox. So when you receive a reply, the last email you got from that conversation comes into the latest one, so you don't see the oldest in your inbox, it's part of your last reply you received...

There is no Rules attached to this account? Something that would delete messages older than...